Method and System for MAC and PHY Synchronization for Energy Efficient Networking

ABSTRACT

Aspects of a method and system for MAC and PHY synchronization for energy efficient networking are provided. In this regard, an interface that enables communication between a MAC controller and a PHY device may be configured to operate in an energy saving mode. While the interface is operating in an energy saving mode, synchronization between the MAC controller and the PHY device may be maintained by one or both of adjusting a clock generated for the interface and/or communicating dummy data via the interface. The clock may be adjusted by one or more of adjusting a frequency of the clock, adjusting an amplitude of the clock, and/or duty cycling the clock. The MAC controller and/or the PHY device may generate the dummy data. The PHY device and/or the MAC controller may discard the dummy data upon receiving the dummy data.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

This patent application is a continuation of non-provisional patentapplication Ser. No. 12/415,978, filed Mar. 31, 2009, which claimspriority to and claims benefit from provisional application No.61/045,203, filed on Apr. 15, 2008.

Each of the above stated applications is hereby incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

Certain embodiments of the invention relate to networking. Morespecifically, certain embodiments of the invention relate to a methodand system for MAC and PHY synchronization for energy efficientnetworking.

BACKGROUND OF THE INVENTION

Communications networks and in particular Ethernet networks, arebecoming an increasingly popular means of exchanging data of varioustypes and sizes for a variety of applications. In this regard, Ethernetnetworks are increasingly being utilized to carry voice, data, andmultimedia traffic. Accordingly more and more devices are being equippedto interface to Ethernet networks. Broadband connectivity includinginternet, cable, phone and VoIP offered by service providers has led toincreased traffic and more recently, migration to Ethernet networking.Much of the demand for Ethernet connectivity is driven by a shift toelectronic lifestyles involving desktop computers, laptop computers, andvarious handheld devices such as smart phones and PDA's. Applicationssuch as search engines, reservation systems and video on demand that maybe offered at all hours of a day and seven days a week, have becomeincreasingly popular.

These recent developments have led to increased demand on datacenters,aggregation, high performance computing (HPC) and core networking. Asthe number of devices connected to data networks increases and higherdata rates are required, there is a growing need for new transmissiontechnologies which enable higher data rates. Conventionally, however,increased data rates often results in significant increases in powerconsumption. In this regard, as an increasing number of portable and/orhandheld devices are enabled for Ethernet communications, battery lifemay be a concern when communicating over Ethernet networks. Accordingly,ways of reducing power consumption when communicating over Ethernetnetworks may be needed.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with some aspects of the present invention asset forth in the remainder of the present application with reference tothe drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A is a block diagram illustrating an exemplary Ethernet connectionbetween two network devices, in accordance with an embodiment of theinvention.

FIG. 1B is a diagram illustrating exemplary network devicescommunicatively coupled via a core device, in accordance with anembodiment of the invention.

FIG. 2 is a diagram illustrating an exemplary MAC/PHY interface thatsupports energy efficient networking, in accordance with an embodimentof the invention.

FIG. 3A is a timing diagram illustrating a EEN enabled MAC/PHY interfacethat maintains synchronization by utilizing a reduced clock frequency,in accordance with an embodiment of the invention.

FIG. 3B is a timing diagram illustrating an EEN enabled MAC/PHYinterface that maintains synchronization by occasionally or periodicallyenabling a clock signal, in accordance with an embodiment of theinvention.

FIG. 3C is a timing diagram illustrating an EEN enabled MAC/PHYinterface that maintains synchronization by occasionally or periodicallyenabling a clock signal, in accordance with an embodiment of theinvention.

FIG. 3D is a timing diagram illustrating an EEN enabled MAC/PHYinterface that maintains synchronization by aperiodically orperiodically communicating dummy data, in accordance with an embodimentof the invention.

FIG. 4 is a flow chart illustrating exemplary steps for reducing powerconsumption of a MAC/PHY interface, in accordance with an embodiment ofthe invention.

DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the invention may be found in a method and systemfor MAC and PHY synchronization for energy efficient networking. Invarious embodiments of the invention, an interface that enablescommunication between a MAC controller and a PHY device may beconfigured to operate in an energy saving mode. While the interface isoperating in an energy saving mode, synchronization between the MACcontroller and the PHY device may be maintained by one or both ofadjusting a clock generated for the interface and/or communicating dummydata via the interface. The clock may be adjusted by one or more ofadjusting a frequency of the clock, adjusting an amplitude of the clock,and/or duty cycling the clock. The clock may be adjusted periodically oraperiodically over one or more time intervals. The interface may beconfigured to operate in an energy saving mode at times determined byone or both of a rate at which data is to be communicated by theinterface and/or an amount of data to be communicated by the interface.The amount of data to be communicated by the interface may be determinedbased on a status of one or more queues in the PHY device and/or the MACcontroller. The interface may exit an energy saving mode when theinterface receives data from the MAC controller and/or when theinterface receives data from the PHY device. The MAC controller and/orthe PHY device may generate the dummy data. The PHY device and/or theMAC controller may discard the dummy data upon receiving the dummy data.

FIG. 1A is a block diagram illustrating an exemplary Ethernet connectionbetween a two network devices, in accordance with an embodiment of theinvention. Referring to FIG. 1A, there is shown a system 100 thatcomprises a network device 102 and a network device 104. The networkdevices 102 and 104 may each comprise a host 106, a media access control(MAC) controller 108, and a PHY device 110. The hosts 106 may becommunicatively coupled to the MAC controllers 108 via interfaces 116 aand 116 b. The MAC controllers 108 may be communicatively coupled to thePHY devices 110 via interfaces 114 a and 114 b.

The network devices 102 and 104 may be link partners that communicatevia the link 112. The network device 102 and/or 104 may comprise, forexample, computer systems or audio/video (A/V) enabled equipment. Inthis regard, A/V equipment may, for example, comprise a microphone, aninstrument, a sound board, a sound card, a video camera, a media player,a graphics card, or other audio and/or video device. Additionally, thenetwork devices 102 and 104 may be enabled to utilize Audio/VideoBridging and/or Audio/video bridging extensions (collectively referredto herein as audio video bridging or AVB) for the exchange of multimediacontent and associated control and/or auxiliary data.

The hosts 106 may each comprise suitable logic, circuitry, interfaces,and/or code that may enable operability and/or functionality of OSIlayers 7 through 3 for packets received and/or to-be-transmitted overthe link 112. The hosts 106 may each comprise, for example, one or moreprocessing subsystems, one or more graphics subsystems, one or moreaudio subsystems, and one or data buses. The hosts 106 may comprise aninterface 116 a for communicating with a MAC controller 108 via a bus120. The data bus 120 may, for example, be a PCI or PCI-X bus.

The MAC controllers 108 may comprise suitable logic, circuitry,interfaces, and/or code that may enable handling of data link layer, OSIlayer 2, operability and/or functionality. The MAC controllers 108 may,for example, be configured to implement Ethernet protocols, such asthose based on the IEEE 802.3 standard, for example. Since each layer inthe OSI model provides a service to the immediately higher interfacinglayer, the MAC controllers 108 may provide the necessary services to thehosts 106 to ensure that packets are suitably formatted and communicatedto the PHY devices 110. The MAC controllers 108 may each comprise aninterface 116 b for communicating with a host 106 via the bus 120. Also,the MAC controllers 108 may comprise one or more memory elements 115 forqueuing received data and/or to-be-transmitted data.

Each of the MAC controllers 108 may also comprise an interface 114 a forcommunicating with a PHY device 110 via a bus 118. The interface 114 amay be, for example, a multi-rate capable interface and/or mediaindependent interface (MII). The interface 114 a may enable transmissionand/or reception of one or more data signals and one or more clocksignals over the bus 118.

The PHY devices 110 may each comprise suitable logic, circuitry,interfaces, and/or code that may enable communication, for example,transmission and reception of data, between the network device 102 andthe network device 104 and may also be operable to implement one or moreenergy efficient networking (EEN) techniques. Each of the PHY devices110 may be referred to as a physical layer transmitter and/or receiver,a physical layer transceiver, a PHY transceiver, a PHYceiver, or simplya PHY. Each of the PHY devices 110 may comprise an interface 114 b forcommunicating with a MAC controller 108 via the bus 118. The interface114 b may be, for example, a multi-rate capable interface and/or mediaindependent interface (MII). The interface 114 b may enable transmissionand/or reception of one or more data signals and one or more clocksignals over the bus 118. Also, the PHY devices 110 may comprise one ormore memory elements 115 for queuing received data and/orto-be-transmitted data.

Each of the PHY devices 110 may be operable to implement one or moreenergy efficient networking (EEN) techniques. For example, the PHYdevices 110 may be operable to support low power idle (LPI) and/orsub-rating, also referred to as subset PHY, techniques. LPI maygenerally refer a family of techniques where, instead of transmittingconventional IDLE symbols during periods of inactivity, the PHY devices110 may remain silent and/or communicate signals other than conventionalIDLE symbols. Sub-rating, or sub-set PHY, may generally refer to afamily of techniques where the PHYs are reconfigurable, in real-time ornear real-time, to communicate at different data rates.

The Ethernet link 112 is not limited to any specific medium. ExemplaryEthernet link 112 media may comprise copper, optical and/or backplanetechnologies. For example, a copper medium such as STP, Cat3, Cat 5, Cat5e, Cat 6, Cat 7 and/or Cat 7a as well as ISO nomenclature variants maybe utilized. Additionally, copper media technologies such as InfiniBand,Ribbon, and backplane may be utilized. With regard to optical media forthe Ethernet link 112, single mode fiber as well as multi-mode fiber maybe utilized. The link 112 may comprise up to four or more physicalchannels, each of which may, for example, comprise an unshielded twistedpair (UTP). The network device 102 and the network device 104 maycommunicate via two or more physical channels comprising the link 112.For example, Ethernet over twisted pair standards 10BASE-T and100BASE-TX may utilize two pairs of UTP while Ethernet over twisted pairstandards 1000BASE-T and 10 GBASE-T may utilize four pairs of UTP. Inthis regard, however, the number of physical channels via which data iscommunicated may vary.

In operation, a bitstream may be communicated between the MAC 108 andthe PHY 110 via the bus 118 and interfaces 114 a and 114 b. Nonetheless,there may, at times, be little or no data being communicated and/orto-be-communicated over the bus 118. During such periods of lowutilization, an energy efficient networking (EEN) control policy mayreconfigure one or both of the interfaces 114 a and 114 b into an energysaving mode. In this regard, because the interfaces 114 a and 114 b mayconsume substantial amounts of energy even when they are not sending orreceiving data, it may be desirable to power down the interfaces duringsuch times. The interfaces may be configured based on an amount of datato be communicated by the interface, a rate at which the data is to becommunicated by the interface, and/or an acceptable latency of datacommunicated by the interface. The amount of data may be determined, forexample, based on a state of one or more queues in the PHY device 110and/or the MAC controller 108. The rate at which the data is to becommunicated may be determined, for example, based on a standardselected during autonegotation and/or selected by an energy efficientnetworking control policy.

Powering down an interface 114 a and/or 114 b may, however, beproblematic because the interfaces may comprise logic, circuitry, and/orcode that may depend on one or more active clock signals to maintainfrequency and/or phase lock. Accordingly, if such clock signals arepowered down, the amount of time required for the interfaces 114 a and114 b to achieve phase and/or frequency lock may introduce prohibitivedelays when attempting to power up the interfaces to send data.Moreover, when additional interfaces are cascaded, e.g., when extenderssuch as XAUI and/or XIF are utilized, the delays in re-establishingcommunications between a series of multiple interfaces 114 a and 114 bmay be cumulative and may make powering down the clock(s) even moreproblematic. Accordingly, aspects of the invention may enable reducingpower consumption of one or both of the interfaces 114 a and 114 b whilereducing the time required to power up the interfaces and achievefrequency and/or phase lock.

In one exemplary embodiment of the invention, a clock signalcommunicated over the bus 118 may continue uninterrupted while otherportions of the interface 114 a and/or 114 b are powered down oroperated in an energy saving mode. In this regard, logic, circuitry,and/or code associated with communicating data over the bus 108 may bepowered down while logic, circuitry, and/or code associated withgenerating the clock signal may remain powered up.

In another exemplary embodiment of the invention, an energy saving clocksignal may be communicated over the bus 118 during time periods that onethere is little or no data to communicate over the bus 118. In thisregard, portions of the interfaces 114 a and/or 114 b, MAC 108 a, and/orPHY 110 a associated with generating a clock signal on the bus 118 maybe operated in an energy saving mode but may remain sufficientlyoperable to generate an energy saving clock signal. The energy savingclock signal may be reduced in frequency and/or amplitude compared tothe conventional clock signal generated while there is data to becommunicated over the bus 118. For example, the frequency may be divideddown or an alternate clock may be utilized while one or both interfaces114 a and 114 b are operating in an energy saving mode. Also, the clocksignal may be generated, at a conventional frequency and/or amplitude,and/or a reduced frequency and/or amplitude, during a portion of a timeinterval and may not be generated for a remaining portion of a timeinterval.

In another exemplary embodiment of the invention, one or both of theinterfaces 114 a and 114 may be powered down during a portion of a timeinterval and may be powered up for a remaining portion of a timeinterval. The interfaces may occasionally “wake up”, generate signals tomaintain frequency and/or phase lock, and then return to an energysaving mode. In this regard, a MAC controller 108 may be operable tooccasionally convey “dummy” data to the interface 114 a to cause theinterface 114 a to exit an energy saving state and generate a clocksignal. Accordingly, the interface 114 b may detect the clock signal andmay exit an energy saving mode re-synchronize to the interface 114 b.The “dummy” data may serve no purpose other than to wake up andsynchronize the interfaces 114 a and 114 b and may thus be dropped bythe PHY 110. Similarly, a PHY device 110 may be operable to occasionallyconvey “dummy” data to the interface 114 b to cause the interface 114 bto come out of an energy saving state and generate a clock signal.Accordingly, the interface 114 a may be operable to detect the clocksignal and may come out of an energy saving mode re-synchronize to theinterface 114 a. The “dummy” data may serve no purpose other than towake up and synchronize the interfaces 114 a and 114 b and may thus bedropped by the MAC controller 108.

In some instances the MAC 108 may be a legacy device and may not supportEEN. In such instances, portions of the PHY 110 a and/or interface 114 bmay be powered down and/or operated in an energy saving modetransparently to the MAC 108. In this regard, the PHY device 110 and/orinterface 114 b may be reconfigured into an energy saving mode thatretains minimum functionality to keep the legacy MAC 108 fromerroneously detecting an error or problem with the PHY device 110. Whilethe EEN PHY 110 is operating in an energy saving mode, it may disregardunneeded and/or legacy signals from the legacy MAC 108. Also, the EENPHY 110 may occasionally generate and convey “dummy” packets to thelegacy PHY 108.

In some instances, waking up the interfaces 114 a and 114 b may requireadditional time from waking up other portions of the network devices. Insuch instances, the additional time to power up the interfaces 114 a and114 b may be communicated to a link partner via packets communicatedover the link 112 and/or utilizing some low-complexity physical layersignaling. For example, the additional time necessary may becommunicated to a link partner utilizing link layer discovery protocol(LLDP) data units. Such LLDP communication may utilized one or morestate machines to ensure communicated information is not stale.

In various embodiments of the invention, a mode of operation of theinterfaces 114 a and 114 b may be controlled via physical layersignaling and or packet communicated over the link 112. In this regard,the control signals and/or packets may be communicated in-band and/orout-of-band with data communicated on the link. Out-of-band controlsignals and/or packets may be communicated via a reserved channel. thecontrol signals may configure one or more registers that may determine amode of operation of the interfaces 114 a and 114 b.

FIG. 1B is a diagram illustrating exemplary network devicescommunicatively coupled via a core device, in accordance with anembodiment of the invention. Referring to FIG. 1B, there is shown thenetwork devices 102 and 104 described with respect to FIG. 1A and thereis shown a core network device 150. The network devices 102 and 104 maybe communicatively coupled via the links 112 a and 112 b, each of whichmay be the same as the link 112 described with respect to FIG. 1A.

The core network device 150 may comprise suitable logic, circuitry,interfaces, and/or code operable to receive and transmit packets via thelinks 112 a and 112 b and additionally to implement an EEN policy. Thecore network device may be, for example, a router, a switch, bridge, ora hub. The device 150 may comprise a plurality of MACs 108 and a PHYs110 which may in turn comprise interfaces 114 a and 114 b, all of whichmay be as described with respect to FIG. 1. In this regard, the corenetwork device 150 may comprise a MAC 108, PHY 110, and an interface 114for each of N network ports, where N may be an integer. Accordingly, thecore network device may be enabled to manage power consumption of up toN interfaces 114 a and 114 b.

In operation, aspects of the invention may be utilized to manage powerconsumption of the interfaces 114 a and 114 b within the device 150. TheMAC controller 108, PHY device 110, and interfaces 114 a and 114 b maybe operable to implement some or all of the aspects of the inventiondescribed with respect to the devices 102 and 104 in FIG. 1A. In variousexemplary embodiments of the invention, one or more clocks associatedwith the interfaces 114 a and 114 b may be slowed down based on theamount of data communicated and/or to-be-communicated between thedevices 102 and 104. For example, the interfaces 114 a and 114 b may beslowed down when one or both of the network devices 102 and areoperating in an energy saving mode.

The network 150 of FIG. 1B illustrates the benefits of various aspectsof the invention. For example, as data is communicated from the device102 to the device 150 and then to the device 104, the data may traversethree of the busses 118. That is, any delay in waking up the interfaces114 a and 114 b may be multiplied by a factor of 3. Accordingly,reducing even small delays in waking up the interfaces 114 a and 114 bmay prevent large delays that accumulate over a network path.

FIG. 2 is a diagram illustrating an exemplary MAC/PHY interface thatsupports energy efficient networking, in accordance with an embodimentof the invention. Referring to FIG. 2, there is shown the interfaces 114a and 114 b described with respect to FIGS. 1A and 1B. Each of theinterfaces 114 a and 114 b may comprise a data processing module 202, acontrol and/or management (Ctrl/Mgmt) module 204, a clock module 206,and a plurality of buffers and/or line drivers (buffers/drivers) 208 ₁,. . . , 208 _(N), 210 ₁, . . . , 210 _(M), and 212 ₁, . . . , 212 _(K).The interfaces are described in generic terms to represent commonfunctions implemented by various interface standards. Exemplarystandards utilized and/or implemented by the interfaces 114 may compriseMII, RMII, GMII, RGMII, SGMII, XGMII, XAUI, and XFI. Additionally, theinterfaces 114 a and/or 114 b may comprise and/or utilize a managementinterfaces such as a management data input output (MDIO) bus.

Each of the data processing modules 202 may comprise suitable logic,circuitry, interfaces, and/or code that may be operable to process datareceived from the MAC controller 108 to make the data suitable forconveyance to the buffers/drivers 208 ₁, . . . , 208 _(N), where N is aninteger. Similarly, the data processing modules 202 may be operable toprocess data received from the buffers/drivers 208 ₁, . . . , 208 _(N)to make the data suitable for conveyance to the MAC controller 108.Exemplary operations performed by the module 202 may comprisemultiplexing, demultiplexing, serialization, and deserialization ofdata. In some embodiments of the invention, a data module 202 may beoperable to generate “dummy” data and convey that data to thebuffers/drivers 208 ₁, . . . , 208 _(N). Similarly, the a module 202 maybe operable to recognize and discard dummy received from thebuffers/drivers 208 ₁, . . . , 208 _(N) data without passing the dataonto the MAC controller 108 and/or higher OSI layers. Data may becommunicated between data modules 202 via the buffers/drivers 208 ₁, . .. , 208 _(N) and the signal lines 214 ₁, . . . , 214 _(N) of the bus118. In this regard, bits of data may be communicated over the bus 118serially or in parallel. Although the data processing modules 202 areillustrated as being within the interfaces 114 a and 114 b, such aphysical boundary may not actually exist in a particular implementationbecause portions of the module 202 may be shared between MAC controllerfunctions and interface functions or between PHY functions and interfacefunctions.

Each of the Ctrl/Mgmt processing modules 204 may comprise suitablelogic, circuitry, interfaces, and/or code that may be operable togenerate and/or process maintenance and/or control information. Invarious exemplary embodiments of the invention, the Ctrl/Mgmt processingmodules 204 may each be operable to read and/or write one or moreconfiguration registers in a PHY device 110. Control and/or managementinformation may be communicated via signal lines 216 ₁, . . . , 216_(M). For example, a single line 216 ₁ may be utilized to read and/orwrite MDIO registers. In various embodiments of the invention, aCtrl/Mgmt processing module 204 may be operable to communicateinformation for implementing EEN techniques and/or protocols. In thisregard, a Ctrl/Mgmt module 204 may be operable to generate signals totrigger synchronization of the interfaces 114 a and 114 b. Also, aCtrl/Mgmt module 204 may be operable to generate signals to trigger aMAC controller 108 and/or PHY 110 to transition into and/or out of anenergy saving mode of operation. Although the Ctrl/Mgmt processingmodules 204 are illustrated as being within the interfaces 114 a and 114b, such a physical boundary may not actually exist in a particularimplementation because portions of the module 204 may be shared betweenMAC functions and interface functions or between PHY functions andinterface functions.

Each of the clock modules 206 may comprise suitable logic, circuitry,interfaces, and/or code that may be operable generate one or more clocksignals on clock lines 218 ₁, . . . , 218 _(K), where K is an integer.In various embodiments of the invention, one or more generated clocksignals may be utilized for one or more of transmission of data,reception of data, transmission of ctrl/mgmt signals, and reception ofctrl/mgmt signals. In various embodiments of the invention, a clockmodule 206 may be operable to generate different clock frequencies fordifferent standards and/or data rates utilized by a PHY 110 device. Forexample, the clock module 206 may generate a 2.5 MHz clock when a PHY110 utilizes a 10 Mb standard such as 10BASE-T, a 25 MHz clock when aPHY utilizes a 100 Mb standard such as 100BASE-T, and a 125 MHz clockwhen a PHY 110 utilizes a 1 Gb standard 1 GBASE-T. Accordingly, aspectsof the invention may enable a clock frequency conventionally utilizedfor a lower standard data rate to be utilized in instances when theinterface is operating in an energy saving mode. To illustrate, a PHY110 may negotiate a data rate of 1 Gbps with a link partner and theclock module 206 may generate a 1.25 GHz clock when operating in anormal mode but may generate a 2.5 MHz or 25 MHz clock when operating inLPI mode. In this regard, switching to a lower frequency clock mayenable maintaining phase and/or frequency lock between the interfaces114 a and 114 b while significantly reducing energy consumption in theinterfaces 114 a and 114 b and on the clock lines 218 ₁, . . . , 218_(K).

The buffers/drivers 208 ₁, . . . , 208 _(N) may comprise suitable logic,circuitry, interfaces, and/or code that may be operable to transmit andreceive signals via the data lines 214 ₁, . . . , 214 _(N). Thebuffers/drivers 210 ₁, . . . , 210 _(M) may comprise suitable logic,circuitry, interfaces, and/or code that may be operable to transmit andreceive signals via the Ctrl/Mgmt lines 216 ₁, . . . , 216 _(M). Thebuffers/drivers 212 ₁, . . . , 212 _(K) may comprise suitable logic,circuitry, interfaces, and/or code that may be operable to transmit andreceive signals via the clock lines 218 ₁, . . . , 218 _(K).

In operation, a transmit clock may clock data into the data module 202,clock the data out of the module 202 into the buffers/drivers 208 ₁, . .. , 212 _(N), and clock the data out of the buffers/drivers 208 ₁, . . ., 212 _(N) onto the data lines 214 ₁, . . . , 214 _(N). In instancesthat there may be no data to transmit across the data lines, transmitportions of the data module 202, transmit portions of thebuffers/drivers 208 ₁, . . . , 212 _(N) may be powered down orreconfigured, and a transmit clock generated by the module 206 may bestopped or reduced in frequency or amplitude. Furthermore, the transmitclock may be stopped and occasionally restarted to maintain phase and/orfrequency lock between the interfaces 114 a and 114 b. Also, thebuffers/drivers 208 ₁, . . . , 212 _(N) may be reconfigured to adjustthe amplitude of the transmit clock signal. In this regard, when thereis no data on the data lines 214 ₁, . . . , 214 _(N), noise may be lessof an issue and a lower transmit clock amplitude may be tolerated.

Similarly, a receive clock on one or more of the clock lines 218 ₁, . .. , 218 _(K) may clock data into the buffers/drivers 208 ₁, . . . , 208_(N) from the data lines 214 ₁, . . . , 214 _(N), clock the data out ofthe buffers/drivers 208 ₁, . . . , 208 _(N) into the data module 202,and clock the data out of the module 202 to higher OSI layers. Ininstances when there may be no data to receive via the data lines,receive portions of the data module 202, receive portions of thebuffers/drivers 208 ₁, . . . , 208 _(N) may be powered down orreconfigured, and a receive clock generated by the module 206 may bestopped or reduced in frequency or amplitude. Furthermore, the receiveclock may be stopped and occasionally restarted to maintain phase and/orfrequency lock between the interfaces 114 a and 114 b. Also, thebuffers/drivers 208 ₁, . . . , 208 _(N) may be reconfigured to adjustthe amplitude of the receive clock signal. In this regard, when there isno data on the data lines 214 ₁, . . . , 214 _(N), noise may be less ofan issue and a lower receive clock amplitude may be tolerated.

In some instances, the receive clock may be recovered from receiveddata. Accordingly, “dummy” data may be occasionally generated by thedata module 202 and conveyed over the data lines 214 ₁, . . . , 214 _(N)to enable frequency and/or phase locking the interfaces 114 a and 114 b.

FIG. 3A is a timing diagram illustrating a EEN enabled MAC/PHY interfacethat maintains synchronization by utilizing a reduced clock frequency,in accordance with an embodiment of the invention. Referring to FIG. 3A,the waveform 302 shows data arriving at an interface. Also shown arewaveforms 304 and 306 show that data being clocked onto the data lines212 ₁, . . . , 212 _(N). In this regard, the waveform 302 may representdata arriving ay an interface 114 a from a MAC 108 or at an interface114 b from a PHY 110.

From time instant T1 until time instant T2, data may be arriving at theinterface, and may be clocked into and processed by the data module 202.This delay between the time instants T1 and T2 may include time requiredto process the data as well time to wake up the interface. Accordingly,the data may need to be queued from the time instant T1 to the timeinstant T2.

At the time instant T2, the processed data may start being clocked ontothe data lines 214 ₁, . . . , 214 _(N). At time instant T3, the data maycease arriving at the interface. At time instant T4, the interface mayfinish clocking the data onto the data lines 214 ₁, . . . , 214 _(N).From the time instant T3 until time instant T5, there may be no data forthe interface to transmit and thus one or more portions of the interfacemay be put into an energy saving mode of operation. Accordingly, fromthe time instant T4 to time instant T6, the transmit clock may bereduced in frequency.

At the time instant T5, the interface may again begin receiving data.From the time instant T5 to time instant T6, the interface may come outof the energy saving mode of operation. In this manner, by maintainingsynchronization via a reduced frequency clock during the time intervalbetween the time instants T4 and T5, the intervals from the time instantT1 to the time instant T2 and from the time instant T5 to the timeinstant T6 may be relatively short enough to prevent the introduction ofprohibitively large path delays, even when the path comprises aplurality of EEN enabled MAC/PHY interfaces.

FIG. 3B is a timing diagram illustrating an EEN enabled MAC/PHYinterface that maintains synchronization by occasionally or periodicallyenabling a clock signal, in accordance with an embodiment of theinvention. Referring to FIG. 3B, waveform 312 shows data arriving at aMAC/PHY interface and waveforms 314 and 316 show that data being clockedonto the data lines 214 ₁, . . . , 214 _(N). In this regard, thewaveform 312 may represent data arriving at an interface 114 a from aMAC 108 or at an interface 114 b from a PHY 110.

From time instant T1 until time instant T2, data may be arriving at theinterface, and may be clocked into and processed by the data module 202.This delay between the time instants T1 and T2 may include time requiredto process the data as well time to wake up the interface. Accordingly,the data may need to be queued from the time instant T1 to time instantT2.

At the time instant T2, the processed data may start being clocked ontothe data lines 212 ₁, . . . , 212 _(N). At time instant T3, the data maycease arriving at the interface. At time instant T4, the interface mayfinish clocking the data onto the data lines 212 ₁, . . . , 212 _(N).From the time instant T3 until the time instant T9, there may be no datafor the interface to transmit and thus one or more portions of theinterface may be put into an energy saving mode of operation.Accordingly, from the time instant T4 to time instant T9, the clock maybe shut down and occasionally or periodically restarted to maintainsynchronization. In this regard, the clock may be restarted from timeinstant T5 to time instant T6 and from time instant T7 to time instantT8.

From the time instant T9 to time instant T10, the MAC/PHY interface mayagain begin receiving data from the MAC and may come out of the energysaving mode of operation. In this manner, because occasionallyre-enabling the clock may maintain synchronization and reduce wake-uptime, the intervals from the time instant T1 to the time instant T2 andfrom the time instant T9 to the time instant T10 may be relatively shortenough to prevent the introduction of prohibitively large path delays,even when the path comprises a plurality of EEN enabled MAC/PHYinterfaces.

FIG. 3C is a timing diagram illustrating an EEN enabled MAC/PHYinterface that maintains synchronization by occasionally or periodicallyenabling a clock signal, in accordance with an embodiment of theinvention. Referring to FIG. 3C waveform 322 shows data arriving at aninterface and waveforms 324 and 326 show that data being clocked ontothe data lines 212 ₁, . . . , 212 _(N). In this regard, the waveform 322may represent data arriving at an interface 114 a from a MAC 108 or atan interface 114 b from a PHY 110.

From time instant T1 until time instant T2, data may be arriving at theinterface, and may be clocked into and processed by the data module 202.This delay between the time instants T1 and T2 may include time requiredto process the data as well time to wake up the interface. Accordingly,the data may need to be queued from the time instant T1 to the timeinstant T2.

At the time instant T2, the processed data may start being clocked ontothe data lines 212 ₁, . . . , 212 _(N). At time instant T3, the data maycease arriving at the interface. At time instant T4, the interface mayfinish clocking the data onto the data lines 212 ₁, . . . , 212 _(N).From the time instant T3 until time instant T5, there may be no data forthe interface to transmit and thus one or more portions of the interfacemay be put into an energy saving mode of operation. Accordingly, fromthe time instant T4 to time instant T6, the transmit clock may bereduced in amplitude.

From the time instant T5 to the time instant T6, the interface may againbegin receiving data and may come out of the energy saving mode ofoperation. In this manner, by maintaining synchronization via a reducedamplitude clock during the time interval between the time instants T4and T5, the intervals between the time instants T1 and T2 and betweenthe time instants T5 and T6 may be relatively short enough to preventthe introduction of prohibitively large path delays, even when the pathcomprises a plurality of EEN enabled MAC/PHY interfaces.

FIG. 3D is a timing diagram illustrating an EEN enabled MAC/PHYinterface that maintains synchronization by occasionally or periodicallycommunicating dummy data, in accordance with an embodiment of theinvention. Referring to FIG. 3D waveform 332 shows a period where nodata is arriving at an interface 114 a or 114 b and waveforms 334 and336 illustrate maintaining synchronization between the MAC and PHY byclocking dummy data onto the data lines 212 ₁, . . . , 212 _(N).

From time instant T1 until time instant T6 there may be no data arrivingat either the interface 114 a or the interface 114 b. Accordingly,during the intervals from time instant T2 to time instant T3 and fromtime instant T4 to time instant T5 dummy data may be generated by theMAC 108 or the PHY 110 and clocked onto the data lines 212 ₁, . . . ,212 _(N). In this manner, the dummy data may cause one or more transmitand/or receive clocks to start-up and the MAC and PHY may beresynchronized.

In this manner one or more clocks generated for an interface 14 a and/or114 b may be duty cycled between a plurality of frequencies. In theexemplary waveform depicted, the clock is duty cycled between is normalfrequency and a zero frequency.

FIG. 4 is a flow chart illustrating exemplary steps for reducing powerconsumption of a MAC/PHY interface, in accordance with an embodiment ofthe invention. Referring to FIG. 4, the exemplary steps may begin withstep 402 when a network device comprising MAC/PHY interfaces 114 a and114 b is powered up. Subsequent to step 402, the exemplary steps mayadvance to step 404.

In step 404, if and when to power down one or more components of thenetwork device may be determined based on an energy efficient networking(EEN) policy. Accordingly, it may be determined to power down all, or aportion of, the interface 114 a and/or the interface 114 b at adetermined time instant. Accordingly, at the determined time instant,the exemplary step may advance to step 406.

In step 406, one or both of the interfaces 114 a and 114 b may beconfigured into an energy saving mode. However, in order to maintainsynchronization between the interface 114 a and the interface 114 b, oneof the techniques described herein may be utilized. In this regard, oneor more clock signal generated may be altered while operating in theenergy saving mode and/or dummy data may be generated while operating inthe energy saving mode. Subsequent to step 406, the exemplary steps mayadvance to step 408.

In step 408, if and when to exit the energy saving mode may bedetermined based on an energy efficient networking (EEN) policy.Accordingly, it may be determined to power up all, or a portion of, theinterface 114 a and/or the interface 114 b at a determined time instant.Accordingly, at the determined time instant the exemplary step mayadvance to step 410.

In step 410, one or both of the interfaces 114 a and 114 b may bereconfigured into a normal or high(er) power mode. In this regard, theinterfaces 114 a and 114 b may become operable to communicated databetween the Mac and PHY at a rate necessary to support the currentactivity of the network device. Subsequent to step 410, the exemplarysteps may return to step 404.

Various aspects of a method and system for MAC and PHY synchronizationfor energy efficient networking are provided. In an exemplary embodimentof the invention, an interface 114 that enables communication between aMAC controller 108 and a PHY device 110 may be configured to operate inan energy saving mode. In one embodiment of the invention, the MACcontroller 108, the PHY device 110, and the interface 114, which enablescommunication between the MAC controller 108 and the PHY device 110, maybe within a communication device. While the interface 114 is operatingin an energy saving mode, synchronization between the MAC controller 108and the PHY device 110 may be maintained by one or both of: adjusting aclock generated for the interface 114 and/or communicating dummy datavia the interface 114. The clock may be adjusted by one or more of:adjusting a frequency of the clock, adjusting an amplitude of the clock,and/or duty cycling the clock. The clock may be adjusted periodically oraperiodically over one or more time intervals. The interface 114 may beconfigured to operate in an energy saving mode at times determined byone or both of: a rate at which data is to be communicated by theinterface 114 and/or an amount of data to be communicated by theinterface 114. The amount of data to be communicated by the interface114 may be determined based on a status of one or more queues in the PHYdevice and/or the MAC controller. The interface 114 may exit an energysaving mode when the interface 114 receives data from the MAC controller108 and/or when the interface 114 receives data from the PHY device 110.The MAC controller 108 and/or the PHY device 110 may generate the dummydata. The PHY device 110 and/or the MAC controller 108 may discard thedummy data upon receiving the dummy data.

Another embodiment of the invention may provide a machine and/orcomputer readable storage and/or medium, having stored thereon, amachine code and/or a computer program having at least one code sectionexecutable by a machine and/or a computer, thereby causing the machineand/or computer to perform the steps as described herein for MAC and PHYsynchronization for energy efficient networking.

Accordingly, the present invention may be realized in hardware,software, or a combination of hardware and software. The presentinvention may be realized in a centralized fashion in at least onecomputer system, or in a distributed fashion where different elementsare spread across several interconnected computer systems. Any kind ofcomputer system or other apparatus adapted for carrying out the methodsdescribed herein is suited. A typical combination of hardware andsoftware may be a general-purpose computer system with a computerprogram that, when being loaded and executed, controls the computersystem such that it carries out the methods described herein.

The present invention may also be embedded in a computer programproduct, which comprises all the features enabling the implementation ofthe methods described herein, and which when loaded in a computer systemis able to carry out these methods. Computer program in the presentcontext means any expression, in any language, code or notation, of aset of instructions intended to cause a system having an informationprocessing capability to perform a particular function either directlyor after either or both of the following: a) conversion to anotherlanguage, code or notation; b) reproduction in a different materialform.

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.

What is claimed is:
 1. A method performed by a network device,comprising: transitioning at least part of the network device from anactive mode to an energy saving mode, the network device including a busbetween a media access control device and a physical layer device,wherein during the energy saving mode, a first part of a media accesscontrol device interface that is coupled to the bus and a first part ofa physical layer device interface that is coupled to the bus are powereddown; and while in the energy saving mode, operating a second part ofthe media access control device interface and/or a second part of thephysical layer device interface in a powered mode that enablesgeneration of an adjusted clock signal that is transmitted across thebus, wherein the adjusted clock signal has a reduced duty cycle that islower than a duty-cycle of a clock generated when the at least part ofthe network device is in the active mode, the adjusted clock signalhaving multiple periodic cycles in a first time period having a reducedfrequency and/or amplitude, and a second time period where no clocksignal is generated.
 2. The method according to claim 1, wherein theadjusted clock signal is generated periodically.
 3. The method accordingto claim 1, wherein the adjusted clock signal is generated aperiodicallyover one or more time intervals.
 4. The method according to claim 1,wherein the adjusted clock signal is reduced in frequency.
 5. The methodaccording to claim 1, wherein the adjusted clock signal is reduced inamplitude.
 6. The method according to claim 1, further comprisingpowering up the first part of the media access control device interfaceand the first part of the physical layer device interface whentransitioning the at least part of the network device from the energysaving mode to the active mode.
 7. A network device, comprising: a mediaaccess control device including a media access control device interface;a physical layer device including a physical layer device interface; anda bus that is connected to the media access control device interface andto the physical layer device interface, wherein upon a transition of atleast part of the network device from an active mode to an energy savingmode, a first part of the media access control device interface and afirst part of a physical layer device interface that is coupled to thebus are powered down, while a second part of the media access controldevice interface and a second part of the physical layer deviceinterface operate in a powered mode that enables generation of anadjusted clock signal that is transmitted across the bus, wherein theadjusted clock signal has a reduced duty cycle that is lower than aduty-cycle of a clock generated when the at least part of the networkdevice is in the active mode, the adjusted clock signal having multipleperiodic cycles in a first time period having a reduced frequency and/oramplitude, and a second time period where no clock signal is generated.8. The network device according to claim 7, wherein the adjusted clocksignal is generated periodically.
 9. The network device according toclaim 7, wherein the adjusted clock signal is generated aperiodicallyover one or more time intervals.
 10. The network device according toclaim 7, wherein the adjusted clock signal is reduced in frequency. 11.The network device according to claim 7, wherein the adjusted clocksignal is reduced in amplitude.
 12. The network device according toclaim 7, wherein the first part of the media access control deviceinterface and the first part of the physical layer device interface arepowered up when the at least part of the network device transitions fromthe energy saving mode to the active mode.
 13. A method, comprising:configuring an interface that enables communication between a mediaaccess control device and a physical layer device to operate in anenergy saving mode upon a transition from an active mode; and while theinterface is operating in the energy saving mode, adjusting a clocksignal generated for transmission over the interface to maintainsynchronization between the media access control device and the physicallayer device, wherein the adjusted clock signal has a reduced duty cyclethat is lower than a duty-cycle of a clock generated when the interfaceoperated in the active mode, the adjusted clock signal having multipleperiodic cycles in a first time period having a reduced frequency and/oramplitude, and a second time period where no clock signal is generated.14. The method according to claim 13, wherein the adjusted clock signalis generated periodically.
 15. The method according to claim 13, whereinthe adjusted clock signal is generated aperiodically over one or moretime intervals.
 16. The method according to claim 13, wherein theadjusted clock signal is reduced in frequency.
 17. The method accordingto claim 13, wherein the adjusted clock signal is reduced in amplitude.